1. Field of the Invention
The invention relates to transesterified copolymers of maleic anhydride with vinyl acetate, particularly useful in the field of detergency and as anti-scaling agents.
2. The state of the art
The action of the sequestering agents in the presence of drinkable water, or of untreated industrial water, is well known. These agents, by formation of complexes with polyvalent metal ions (for instance alkaline-earth metal ions), which form the water hardness, and even with other heavy ions, hinder the formation of precipitates, thus avoiding the scale (incrustation) deposition. In plants where water is warmed, such as boilers or heat-exchangers, the above mentioned agents hinder, as is known, the scale formation on the metal surface. During home-washing and industrial cleaning, polyvalent metal ions may interact with the anions present in the soil and with the anions dissolved by the detergent. In this case also, the scaling (incrustation) action of the mentioned agents on the fabric fibers is known. When control agents are not present, the incrustation would increase the ash contents, washing by washing, thus causing undesired matting and grey coloration phenomena.
A compound used since many years (showing an excellent activity against the formation of precipitates and inhibiting the re-deposition of solid particles and soil on fabrics) is sodium tripolyphosphate. However, it is known that such compound, by degradation in water, gives rise to phosphates, which in turn favor the anomalous growth of algae in inland waters and seas. Thus contributes to the phenomenon known as eutrofication and to the consequent reduction (in the most serious cases exhaustion) of the oxygen contents in waters, with imaginable ecologic consequences. That is why, in many countries, laws were introduced to limit or to forbid the use of sodium tripolyphosphate in detergents. Other compounds having a fair complexing and anti-precipitation activity against soil (and insoluble salts) are aminocarboxylic acids. We mention for instance the sodium salts of nitrilotriacetic acid (NTA) and of ethylenediaminotetracetic acid (EDTA). However, these compounds show some drawbacks, limiting their use, such as the presence of nitrogen in the molecule nitrogen, in fact, has a role in the eutrofication process. Therefore, their use can be only a restricted use. The reduction of the Na-tripolyphosphate contents in detergents has become possible by the use of gradually increasing amounts of Zeolite 4A (a particular sodium aluminosilicate) with substitution ratios higher that 1:1, on sodium tripolyphosphate. In order to get a more effective and complete activity of the detergent formulations having low phosphorous contents, the contemporary presence of other agents, different from zeolite, and/or coadjuvants of detergency, showing a particular action, is also requested.
The Applicants have now found new and more effective chemical intermediates, which do not contain either phosphorus or nitrogen atoms in their structure and which are consisting only of C, H and O atoms, exhibiting a fair effectiveness, so that they can be used as sequestering agents, or generally as coadjuvants, and furthermore as anti-scaling agents in processes involving the heating of drinkable and industrial waters. Furthermore, the new intermediates can be used with a great advantage in detergency processes, where the presence of alkaline-earth ions, already in the cold, may give rise to the precipitation of insoluble salts, because of the interaction of some components of the detergent and as the result of heating processes, thus forming precipitates typical of the hard waters. These intermediates are particular derivatives of the maleic anhydride-vinyl acetate copolymers, hereinafter MA-VA copolymers, which show superior technological properties in comparison with the (hydrolized) copolymers used in the past and described for instance in U.K. Patent No. 1,385,131.